Devices for heating non-metallic materials in an electromagnetic radiation field



1969 H. A. PUSCHNER DEVICES FOR HEATING NON-METALLIC MATERIALS IN ANELECTROMAGNETIC RADIATION FIELD Filed March 13, 1967 Fig.4

United States Patent ,0

3,474,208 DEVICES FOR HEATING NON-METALLIC MA- TERIALS IN ANELECTROMAGNETIC RA- DIATION FIELD Herbert August Puschner, OsterholzerHeerstrasse 175, Bremen, Germany Filed Mar. 13, 1967, Ser. No. 622,696Int. Cl H05b 9/06, 5/00 US. Cl. 219- 10.55 9 Claims ABSTRACT OFDISCLOSURE This invention'relat es to a device for heating web shapednon-metallic materials or bulk goods in an electromagnetic radiationfield.

It is known toheatweb shaped non-metallic materials, for example textileor paper -webs,- by passingv them through a meander shaped waveguide. Adevice serving for such a purpose has been proposed whichisc'oristructed from a rectangular waveguide bent into meander shape,the waveguide being slotted to a width of several millimeters on itswide side,along the axis of symmetry. Web shaped goods to be heated areguided through the slot. The bending of the electromagnetic wave through180 takes place in rounded or angular knee portions, the disturbanceregions of which are compensated by known compensation means, forexample pins and apertures, in order to avoid standing waves along theline. As a rule, the slots terminate in front of the waveguide kneeportions, where as a result of these transition regions, supplementaryreflections occur which have to be compensated. It is very diflicult toexclude all reflections over a wide band in this device. Standing wavesof low amplitude, particularly when treating synthetic plastics andperforming similar steps, where temperature ranges of a few degreescentigrade have to be adhered to, lead to non-uniformities in heating ofthe material. Moreover, with slot widths of more than 5 mm., radiationlosses and couplings between adjacent waveguides occur, which can leadto standing waves. As a result of this, thick webs cannot be heated.

In most processes which can be performed using meander shapedwaveguides, the steam which occurs has to be extracted from thewaveguide. Slots in the waveguide wall are disturbance regions, whichcan cause reflections. Moreover, as a result of the complicatedconstruction of the previously proposed device, satisfactory ventilationcan be achieved only with considerable difficulties. Also, themechanical construction of such a device is very diflicult andconsequently expensive, for large web widths.

The present invention consists in a device for heating web shapednon-metallic materials or bulk goods in an electromagnetic radiationfield, comprising a waveguide formed by an inner conductor and flatrectangular outer conductors, the inner conductor and the outerconductors enclosing the treatment space between them, the innerconductor being periodically bent so as to have a meander shaped,sinuous or trapezium form the amplitude of which is smaller than thewidth of the outer conductors, the ends of the inner conductor beingguided out from between the outer conductors and being connected toinner "ice conductors of coaxial lines the outer conductors of which areelectrically conductively connected with the outer conductors.

Such a device is very simple to construct. Reflections at the bends ofthe inner conductor can by suitable shaping be kept to such small valuesthat practically on a progressive wave is propagated. Radition losses,such as occur with meander shaped waveguides, cannotoccur. The heatingof thick webs presents no difliculties since the entire intermediatespace between the inner and outer conductor is available for passage ofthe goods. More especially, the device of the invention has greatadvatnages as a result of the possibility of double conveyance at thetwo sides of the inner conductor. Moreover, ventilation of the interioris simple, if the outer conductor is made of a perforated plate. Aplurality of these devices may be arranged perpendicularly alongsideeach other and the web shaped material, for example textile webs printedon one side, can be fed in a freely suspended manner through theindividual devices, over reversing rollers.

The device of the invention is suitable not only for heating web shapedmaterials, but more particularly with a perpendicular arrangement, isalso suitable for heating bulk goods. With such an arrangement, theinner conductor is covered on both sides with plates of low lossdielectric so that the bulk material slides between smooth walls. 7 Inorder to make the invention clearly understood, reference will now bemade to the accompanying drawings which are given by way of example andin which:

FIG. 1 is a perspective view of a device of the invention;

FIG. 2 is a longitudinal section througha horizontally arranged deviceaccording to FIG. 1, for web shaped materials;

FIG. 3 is a longitudinal section through a perpendicularly arrangeddevice according to FIG. 1; and

FIG. 4 is a longitudinal section through a perpendicularly arrangeddevice for bulk goods.

In FIG. 1, an inner conductor 1 which is periodically bent in a sinuousshape is arranged with equal spacings between two flat outer guideplates 2, which are connected at two oppositely lying sides in each caseby a metal wall 3 so that a common tubular outer guide 2, 3 with anarrow rectangular cross section is produced which encloses all of theconvolutions of the inner conductor 1. The material to be heated, forexample web shaped material 4 (see FIG. 3) runs through the device inthe Z direction 5. The amplitude of convolution of the inner conductor 1is smaller than the overall width of the outer conductor 2, 3. Both ends8, 9 of the inner conductor 1 merge into coaxial lines 10, 11. Amicrowave generator 12 is connected to the coaxial line 10, and theother coaxial line 11, if the inner conductor 1 does not terminate atthe side wall 3, is provided with a termination load 13 which receivesthe non-absorbed electromagnetic energy.

The two intermediate spaces between the inner conductor 1 and theexternal conductor plates 2, 2 in each case form a chamber 14 of thetreatment space for the material to be treated.

A web 4 to be heated, is for example guided through both chambers 14 onboth sides of the inner conductor 1.

In FIG. 2, the mounting 15 for the inner conductor 1 can be seen. Themounting 15 is of low loss synthetic plastics material and compensatesthe disturbance regions of the bends 16. The outer conductor 2, 3extends at the inlet and outlet openings 17, 18 beyond the innerconductor 1 by several Wavelengths, in order that the openings 17, 18are free of radiation as a result of sulficiently high damping of thewaveguide.

In FIG. 3 a plurality of devices according to FIG. 1 are arrangedvertically alongside each other, the web shaped material being guidedtherethrough in a freely suspended manner, over reversing rollers 19.

A similar arrangement to FIG. 3 is shown in FIG. 4. This device can beused for heating bulk goods 20. For this purpose, the inner conductor 1.is-covered on both sides by synthetic plastics plates 21 of low lossmaterial, in order to provide walls 22.

What I claim is:

1. A device for heating web shaped non-metallic mate rials or bulk goodsin an electromagnetic radiation field, comprising a waveguide formed byan inner conductor between two flat rectangular outer conductors, theinner conductor and the outer conductors enclosing the treatment spacebetween them, the inner conductor being periodically bent so as to havea meander shaped, sinuous or trapezium form the amplitude of which issmaller than the width of the outer conductors, the ends of the innerconductor being guided out from between the outer conductors and beingconnected to inner conductors of coaxial lines the outer conductors ofwhich are electrically conductively connected with the outer conductors.

2. A device as claimed in claim 1, wherein edges of chambers 14 withsmooth the outer conductors which run parallel to the axis of symmetryof the periodicallybent inner conductor are electrically .conductivelyconnected with each other by metal plates in which transition openingsare provided for the outwardly extending coaxial lines.

3. A device as claimed in claim 1, wherein the outer condn'ctors extendby a plurality of wavelengths beyond the inner conductor in thedirection of the axis of symmetry of the periodically bent innerconductor.

4. A device as claimed in claim 1, wherein the outer conductors consistof perforated plates. 5. A device as claimed in claim 1, wherein theinner conductor is covered on its sides facing the outer conduetors withplates of low loss synthetic plastics material.

6. A device as claimed in claim 1, wherein the inner conductor issurroundedbya layerv .ofdiel-ectric material; 7. Apparatus for heatingweb-shaped non-metallic" materials and bulk goods in an electromagneticradiation field comprising,

first and second generally"parallel outer conductors,

a' meander-shaped inner conductor insjt'llatedly sepafirst and secondouter tors comprise heating chambers for the material tofbe treated. a

9. Apparatus in accordance with claim 7 wherein said first and secondouter conductors comprise perforated plates.

References Cited UNITED STATES PATENTS 2,442,114 5/1948 Brown 2l910.55 X3,235,702 2/1966 Timmermans et al. 219--l0.55 3,307,010 2/1967 Piischner219-1055 FOREIGN PATENTS 1,484,860 5/1967 France;

JOSEPH 'V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner US.Cl; X.R.

